The preparation of 3-exomethylenecephams has recently been reported [Chauvette, R.R., and Pennington, P.A., Journal of Organic Chemistry, 38, 2994 (1973); and Chauvette, R.R., and Pennington, P.A., Journal of the American Chemical Society, 96, 4986 (1974)]. In conjunction with this disclosure, it was also reported that the 3-exomethylenecephams could be converted by ozonolysis to their corresponding 3-"oxo" cephams. These latter compounds can also be termed 3-keto cephams or, in terms of their tautomeric form, 3-hydroxy cephems.
It has now been discovered that 3-exomethylenecephams and 3-ketocephams can be prepared from a novel class of azetidin-2-ones. It is to such a class of compounds as well as to a process for preparing 3-exomethylenecephams and 3-ketocephams from these compounds that this invention is directed.